It is known in the field of computed radiography that phosphor sheets are supplied via cassettes from which they are pulled and their latent image is scanned in a reader. (See, for example, U.S. Pat. Nos. 5,124,550 and 5,186,338). It is critical, when the cassettes and sheets are fed to the reader that the sheet "not be exposed to undesirable light" so as "to prevent image degradation" (column 1 of the '550 patent). Hence, shielding is provided around the cassette as it is clamped in the reader. Because most readers come with a single-sized opening and appropriate shields therefor, but cassettes come in multiple sizes, it is also common to mount the variously-sized cassettes on a single-sized pallet for insertion into the reader, as per U.S. Pat. No. 5,186,338.
Although such pallets work well, they do have a drawback: They provide an additional expense and handling requirement. It would be advantageous, instead, to be able to feed the variously-sized cassettes directly into the reader. However, this has been difficult, if not impossible, as the width of the reader slot not occupied by a smaller cassette creates a light-leak.
U.S. Pat. No. 4,363,548 does describe one attempt to overcome this problem. To allow two smaller size cassettes to be used (without a pallet), a removable insert is used in the reader slot having two separate smaller slots each of which is shuttered. Only the slot actually occupied by its appropriately sized cassette ends up opening a shutter, and since the cassette is the proper size, light-shielding is maintained. However, a solid frame member 30 separates the two slots and shutters, so that the insert must be removed when the large-size cassette is to be inserted.
Thus, prior to this invention there has been a problem in providing a reader for a phosphor screen from a cassette of varying size, without the use of a pallet or a removable insert which creates shuttered slots sized only for the smaller cassettes.